High demand exists for mobile computing devices that can be used anywhere anytime. One limitation placed on this demand are the displays used in these devices.
Conventional mobile computing devices use backlit displays to display text or an image. One such display is a liquid crystal display. These displays use a variety of liquid crystal substances that have a unique feature of being affected by electrical current. For example, a particular form of liquid crystal is the nematic liquid crystal called twisted nematics which are naturally twisted. Applying an electric current to these crystals will untwist them to varying degrees depending on the voltage. Because the crystals react predictably to electric current, the electric current can be used to control the passage of light through the crystal.
Liquid crystals do not emit light of their own. External lighting must be applied to the crystal in order that light from the crystal can be seen. Backlighting may be provided by any light source such as a fluorescent tube, LEDs, lasers, or other sources of light. In conventional backlit displays used on mobile computing devices, the computer display is typically lit with built-in fluorescent tubes typically located behind the LCD. Depending upon the orientation of the liquid crystals under the influence of an applied voltage, there is more light or less backlight that is allowed to pass through the crystals. That provides the dark and light points of light coming from the liquid crystal display that together form the text or image that is seen on the display screen by the user.
The readability of back lit displays is generally inversely proportional to ambient light. This is because the lighting for backlit display comes from the backlight. When the ambient light is dark or where lighting is scarce, there is no or little light reflecting off the liquid crystal display to interfere with the backlighting that is shining through the liquid crystal display. For that reason, a backlit display can be easily read in the dark or where lighting is scarce. Where, however, the ambient light is too strong, the readability of the backlit display degrades on account of the interference between the strong ambient light reflecting off of the liquid crystal display and the backlight that is coming from the liquid crystal display. In addition, the human eye responds to high ambient light by closing the iris resulting in making the light in the back light display appear dimmer. For these reasons, backlit displays are difficult to read when the ambient or outdoor light is strong. In direct sunlight, such as on the beach, the interference may be so great that the backlit display may be impossible to read.
A relatively new technology for displaying text and images that is becoming increasing popular on account of e-books is electronic paper. Electronic paper, e-paper and electronic ink are display technologies which are designed to mimic the appearance of ordinary ink on paper. Unlike conventional backlit flat panel displays which emit light, electronic paper displays reflect light like ordinary paper. Other applications of electronic visual displays include electronic pricing labels in retail shops, and digital signage, time tables at bus stations, electronic billboards, and e-paper magazines. Some devices, like USB flash drives, even use electronic paper to display status information, such as available storage space. E-ink is less popular with cell phones although Motorola makes one cell phone with an e-ink display known as the E3.
Diffuse reflecting technology, such as e-ink, is particularly useful for e-books because it has low refresh rates compared to other low-power display technologies, such as LCD. The low refresh rates allow for a more stable image, since there is no need to refresh the image constantly which can make an e-ink display more comfortable to read. The low refresh rates also reduce the power requirements for displaying text and images. Indeed, some e-ink technologies require very little or no refresh at all and so can even hold the static text and images indefinitely without using electricity, except when changing to another image. The technology of e-ink can also allow for a wider viewing angle than is possible with an LCD display.
The low refresh rate possible with e-ink however makes e-ink displays not well suitable for sophisticated interactive applications, such as fast moving menus, mouse pointers or scrolling. For example, a document displayed using e-ink cannot be zoomed quickly or smoothly without some blurring. This is one reason why computing devices such as laptops, tablets, and mobile devices tend to use LCD displays and not e-ink for the display
Both the LCD and the e-ink displays illustrate how conventional computing devices are indeed limited by their display to when and where they can be used. The readability of e-ink displays improve with stronger ambient light while the readability of LCD displays degrades in those conditions. The LCD displays are most readable when there is low or no ambient light. The e-ink displays cannot be read in those conditions. The low refresh rates for e-ink allow for a more stable image. However, those low refresh rates inhibit the use of e-ink with sophisticated interactive applications. The paradox is that when outside and the sun is shining, one person is unable to see a thing on his backlit computer while the other is reading his book on a Kindle™ with the e-ink. Similarly, a delivery woman has no problem reading the e-ink on an e-ink display. But she has to take off her sunglasses and shelter the display from the direct sunlight in order to see anything on a backlit display.
There is a need to meet the high demand for mobile computing devices that can be used anywhere anytime under wider lighting conditions, with more sophisticated interactive applications, and with lower power requirements. This disclosure addresses that need.